Systems and methods for pedicle screw implantation using flexible drill bit

ABSTRACT

A method of implanting a bone anchor in a vertebra comprises engaging a tip of a flexible drill bit with boney structure of the vertebra, rotating the flexible drill bit at a slow speed, pushing the drill bit into exterior cortical bone of the boney structure of the vertebra, guiding the flexible drill bit into cancellous bone of the vertebra, receiving a tactile output generated by the flexible drill bit indicating resistance of interior cortical bone of the boney structure against the flexible drill bit, and reorienting a trajectory of the flexible drill bit toward the cancellous bone of the vertebra in reaction to the tactile output.

TECHNICAL FIELD

This document pertains generally, but not by way of limitation, tosystems and methods for bone anchor implantation. More specifically, butnot by way of limitation, the present application relates to pediclescrew implantation using powered drill bits.

BACKGROUND

A spinal column can require correction of spinal deformities andabnormalities resulting from trauma or degenerative issues. Variousmethods of correcting issues with the spinal column can include fusingadjacent vertebrae together or immobilizing the spinal column with a rodsystem. For example, fasteners or other fixation devices can be attachedto each vertebra, with each fastener serving as an anchor point forattaching the rod. Rods can be placed on either side of the spinalcolumn to span several vertebrae. The fasteners are carefully insertedinto the vertebrae at a pedicle area of the bone. Ideally, thetrajectory of the fastener is controlled to ensure the fastener passesstraight through the pedicle into the vertebral body withoutintersecting the vertebral foramen where the spinal cord is located.However, inexperience or unusual bone conditions can infrequently leadto undesirable penetration or near penetration of the vertebral foramen,which can sometimes result in harm to the patient. A surgeon typicallyrelies on personal understanding of spinal anatomy and skill to placeeach fastener. Typically, each fastener is inserted manually after firsttapping the pedicle with a manual pilot drill. Some spinal correctionprocedures can involve placement of many fasteners, which can result insurgeon fatigue.

Examples of methods for pedicle screw implantation are described in U.S.Pat. No. 6,849,047 to Goodwin; U.S. Pat. No. 9,549,744 to Pommer et al.;and U.S. Pub. No. 2017/0181774 to Cahill. U.S. Pub. No. 2013/0296864 toBurley et al. describes a flexible drill bit for use in minimallyinvasive orthopedic procedures.

OVERVIEW

The present inventors have recognized, among other things, that aproblem to be solved can include the inability of surgeons to readilyfeel placement of a drill bit when implanting a pedicle screw,particularly in powered drill applications. Specifically, the presentinventors have recognized that the use of powered drilling in the spinalcolumn has been avoided by surgeons due to loss of tactile feedbackcompared to manual drilling procedures. For example, the aforementionedpublication to Cahill teaches away from the complete use of powereddrilling when implanting pedicle screws due to loss of tactile feel. Assuch, fatigue associated with repeated manual drilling operations canresult in inaccurate pedicle screw placement as well as a reducing inthe number of surgeries that can be safely performed in a particulartime period.

The present subject matter can help provide a solution to this problem,such as by providing tactile feedback of a powered drill bit used forpedicle screw implantation. In particular, powered drilling of vertebralpilot channels can be performed using a flexible drill bit the transmitstactile sensation to the surgeon, thereby permitting the surgeon to feeldifferences in cortical and cancellous bone through the drill bit evenwhen being rotated by an external power source. The flexible drill bitcan be rotated at slow speeds, e.g., one to three revolutions persecond, to facilitate transmission of tactile feel from the bone to thehand of the surgeon. The flexible drill bit can be rotated slow enoughso that the force of the impact of a cutting head of the flexible drillbit on cortical bone is not overwhelmed and muted out by the speed ofthe cutting head cutting through the cortical bone. Additionally, thediameter of the shaft of the flexible drill bit can be sized to permitthe cutting head to deflect upon impact with cortical bone and transmita vibration associated with the impact through the drill bit.

In an example, a method of implanting a bone anchor in a vertebracomprises engaging a tip of a flexible drill bit with boney structure ofthe vertebra, rotating the flexible drill bit at a slow speed, pushingthe drill bit into exterior cortical bone of the boney structure of thevertebra, guiding the flexible drill bit into cancellous bone of thevertebra, receiving a tactile output generated by the flexible drill bitindicating resistance of interior cortical bone of the boney structureagainst the flexible drill bit, and reorienting a trajectory of theflexible drill bit toward the cancellous bone of the vertebra inreaction to the tactile output.

In another example, a method of implanting a pedicle screw into apedicle of a vertebra comprises determining a trajectory for a pediclescrew shaft into a cancellous bone canal behind a cortical bone wall toavoid interior cortical bone, engaging a tip of a drill bit having atapered shaft with a starting point of the trajectory on the corticalbone wall of the pedicle of the vertebra, rotating the drill bit usingrotational input from a powered driver, pushing the powered driver topenetrate the tip of the drill bit through the cortical bone wall alongthe trajectory, guiding the drill bit into the cancellous bone canal,sensing engagement of the tip of the drill bit with the interiorcortical bone, and reorienting the drill bit along the trajectory awayfrom the interior cortical bone.

In yet another example, a sliding sleeve can be used in conjunction withpowered shafts of the present disclosure. For example, a sliding sleevecan be used with a powered pedicle screw driver shaft to provide alocation for a surgeon to grasp, and thereby guide and steady, thedriver shaft. In another example, a sliding sleeve can be used with apowered flexible drill bit to provide a location for receiving tactilefeedback from the flexible drill bit, in addition to providing alocation for a surgeon to grasp, and thereby guide and steady, theflexible drill bit.

This overview is intended to provide an overview of subject matter ofthe present patent application. It is not intended to provide anexclusive or exhaustive explanation of the invention. The detaileddescription is included to provide further information about the presentpatent application.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded view of a powered drill bit system comprising apowered driver, a gear system and a drill bit.

FIG. 2 is a side view of an embodiment of the drill bit of FIG. 1comprising a flexible drill bit comprising a cutting head, a flexibleshaft and a coupling portion.

FIG. 3A is a first close-up side view of the cutting head of theflexible drill bit of FIG. 2 showing a gash angle for cutting surfacesfor use in cutting bone.

FIG. 3B is a second close-up side view of the cutting head of theflexible drill bit of FIG. 2 showing a rake angle for cutting surfacesfor use in cutting bone.

FIG. 4 is a close-up view of the coupling portion of the flexible drillbit of FIG. 2 showing torque transfer and retaining features.

FIG. 5 is a close-up side view of the cutting head and flexible shaft ofFIG. 2 showing graduation marks and bands that can be used for depthcontrol.

FIG. 6 is an exploded view of the powered driver of FIG. 1 shown with agear system, a pedicle screw driver shaft, a sliding sleeve device and apedicel screw.

FIG. 7 is a perspective view of the sliding sleeve device of FIG. 6.

FIG. 8 is a side cross sectional view of the sliding sleeve device ofFIG. 7 taken at section 8-8.

FIG. 9 is an end cross-sectional view of the sliding sleeve device ofFIG. 7 take at section 9-9.

FIG. 10 is a diagrammatic superior view of a cross-section of a vertebrashowing a probe inserted into a pedicle for preparation of a pilot drillbit.

FIG. 11 is a diagrammatic view of the vertebra of FIG. 10 showing theflexible drill bit of FIGS. 2-5 inserted into the pedicle to form apilot hole.

FIG. 12 is a diagrammatic view of the vertebra of FIG. 11 showing areamer probe inserted into the pilot hole of FIG. 11 to widen the pilothole.

FIG. 13 is a diagrammatic view of the vertebra of FIG. 12 showing a tapinserted into the widened pilot hole to form threading on a pediclescrew hole.

FIG. 14 is a diagrammatic view of the vertebra of FIG. 13 showing asounding probe inserted into the pedicle screw hole of FIG. 13 toconfirm pedicle integrity of the pedicle screw hole.

FIG. 15 is a diagrammatic view of the vertebra of FIG. 14 showing apedicle screw being inserted into the pedicle screw hole using a powereddriver shaft with a sliding sleeve device.

FIG. 16 is a line diagram illustrating steps of a method for forming apilot hole using a flexible drill bit and a powered driver in accordancewith the systems and methods described herein.

In the drawings, which are not necessarily drawn to scale, like numeralsmay describe similar components in different views. Like numerals havingdifferent letter suffixes may represent different instances of similarcomponents. The drawings illustrate generally, by way of example, butnot by way of limitation, various embodiments discussed in the presentdocument.

DETAILED DESCRIPTION

FIG. 1 is an exploded view of powered drill bit system 10 comprisingpowered driver 12, gear system 14 and drill bit 16. Powered driver 12can comprise motor housing 18, handle 20, first control trigger 22A,second control trigger 22B, gear system socket 24, gear system lock 26and battery lock 28. Gear system 14 can comprise housing 30 in which canbe disposed a gear system (not shown). Housing 30 can also comprisedrill bit socket 32 as well as features for engaging socket 24, such aschannel 34 and teeth 36. Housing 30 can also include features (notshown) at socket 32 for engaging and retaining drill bit 16. Drill bit16 can comprise proximal end 38 that can include features for engagingsocket 32, distal end 40 that can include features for removing bone,and intermediate portion 42 that can include a flexible shaft that isadapted for performing implantation of bone anchors such as pediclescrew shafts.

Powered drill bit system 10 can be used to perform pedicle screwimplantation procedures as described herein, as well as otherprocedures. Powered driver 12 can be used to generate rotational outputfor rotating drill bit 16, among other attachments. For example, one orboth of control triggers 22A and 22B can be actuated to cause a motor(not shown) within motor housing 18 to rotate. Control trigger 22A canbe configured to generate low speed rotation at socket 32 in a firstdirection and trigger 22B can be configured to cause high speed rotationat socket 32 in the first direction, such as by controlling the amountsof electrical powered delivered from a battery (now shown) within handle20 to the motor. Additionally, control triggers 22A and 22B can besimultaneously depressed to cause rotation of socket 32 in the oppositedirection as the first direction. Additionally, control triggers 22A and22B can variably control the speed of the motor based on theirdisplacement. For example, further depressing control triggers 22A and22B toward handle 20 can cause faster rotational output of the motor.

Gear system lock 26 can comprise a button or lever that can engagechannel 34 of housing 30 to prevent displacement of gear system 14 alongrotational axis A. Teeth 36 of housing 30 can engage mating teeth 44 insocket 24 to prevent rotation of housing 30 about rotational axis A.Socket 32 can rotate within housing 30 via engagement with the motor inhousing 18. Gear system lock 26 can be depressed to permit gear system14 to be removed from socket 24. Gear system 14 can be used to reduce,or otherwise change, the output speed of powered drill bit system 10.For example, gear system 14 can include a gear train that receives inputfrom the motor in housing 18 and reduces that speed to an output speedthat is input into socket 32, thus causing drill bit 16 to rotate at aspeed slower than the motor. Using gear system 14 as a gear reductionsystem provides a surgeon with additional control over the slow speedoperation of the drill bit or other instrument attached to the powereddrill bit system 10. For example, in one configuration, gear system 14can be configured to limit rotational output of flexible drill bit 16 toa safe speed for pilot hole drilling in a pedicle, and flexible drillbit 16 can include can include proximal end 38 that can be configured toonly mate with gear system 14.

As is discussed in greater detail with reference to FIG. 2, proximal end38 can include features for engaging socket 32 to maintain connection ofdrill bit 16 to gear system 14, and distal end 40 can include featuresfor removing bone. Intermediate portion 42 can comprise a flexibleportion that is configured to transmit rotational shaft power fromproximal end 38 to distal end 40, while permitting proximal end 38 to bedisplaced off-axis from proximal end 38 while rotating. Flexing ofintermediate portion 42 can be detected by a user of powered drill bitsystem 10. As such, the user of powered drill bit system 10 can receivetactile feedback when drill bit 16 flexes, such as when drill bit 16transitions from engaging a first substance with a first density toengaging a second substance with a second, lower density, such ascortical and cancellous bone. In a specific example, the off-axisdisplacement characteristics are configured to permit distal end 40 tocut cortical and cancellous bone when sufficient axil force is appliedto drill bit 16 by a user, while also allowing distal end 40 to bedisplaced off-axis when distal end 40 engages cortical bone from theside. As discussed below with reference to FIGS. 6-9, sliding sleeve 78can be used with system 10. In various embodiments, sliding sleeve 78can be used to receive or enhance the perception of the tactile feedbackgenerated by flexible drill bit 16, in addition to providing a locationfor the surgeon to grasp flexible drill bit 16 to guide and steadyflexible drill bit 16.

FIG. 2 is a side view of an embodiment of drill bit 16 of FIG. 1comprising proximal end 38, distal end 40 and intermediate portion 42.Proximal end 38 can comprise flat 46 and channel 48. Distal end 40 cancomprise cutting head 50. Intermediate portion 42 can comprise firstdrive shaft 52, neck 54 and second drive shaft 56. FIG. 3A is a firstclose-up side view of cutting head 50 of flexible drill bit 16 of FIG. 2showing gash angle α1 for cutting surfaces for use in cutting bone. FIG.3B is a second close-up side view of cutting head 50 of flexible drillbit 16 of FIG. 2 showing rake angle α2 for cutting surfaces for use incutting bone. FIG. 4 is a close-up view of proximal end 38 of flexibledrill bit 16 of FIG. 2 showing flat 46 and channel 48. FIGS. 2-4 arediscussed concurrently.

Flat 46 and channel 48 can be used to retain drill bit 16 within socket24 (FIG. 1). For example, flat 46 can engage a rotating drive member ofgear system 14, which is coupled to powered driver 12 and can beconfigured to receive torque from the rotating drive member and transmitthe torque to first drive shaft 52. Channel 48 can engage with aretaining member of powered driver 12 and can be configured to resistaxial displacement of drill bit 16 along rotational axis A. For example,ball bearings within socket 24 can be pushed into channel 48 to inhibitaxial displacement while permitting rotation along rotational axis A.

First drive shaft 52 can extend from proximal end 38 along rotationalaxis A. Drive shaft 52 can comprise an elongate body configured totransmit torque from proximal end 38 to neck 54. In an example, driveshaft 52 can comprise a cylindrical body, but can have otherconfigurations such as hexagonal. Neck 54 can comprise a transition bodybetween first drive shaft 52 and second drive shaft 56. Neck 54 can beconfigured to reduce stress that might otherwise result in an abrupttransition between the different sizes of first drive shaft 52 andsecond drive shaft 56. Neck 54 can have a conical shape, but cancomprise other configurations such as curved or sloped surfaces thatsmoothly blend together. As discussed below, neck 54 can also include acurved surface to transition into second drive shaft 56 with producingan edge or stress concentration. Second drive shaft 56 can extend fromneck 54 along rotational axis A. Drive shaft 56 can comprise an elongatebody configured to transmit torque from proximal neck 54 to cutting head50. In an example, drive shaft 56 can comprise a cylindrical body, butcan have other configurations such as hexagonal. Cutting head 50 caninclude one or more cutting flutes, such as flutes 58A and 58B, that areshaped to form edges configured to cut bone. Cutting head 50 can bebulbous compared to the diameter of drive shaft 56 or can have the samediameter as drive shaft 56.

Drill bit 16 is sized and shaped, and made from a desired material, toperform with desired mechanical properties to transmit torque to cuttinghead 50 from proximal end 38, while also permitting flexure of seconddrive shaft 56 and transmission of vibration from cutting head 50 toproximal end 38. In examples, drill bit 16 can be fabricated from arigid material that transmits torque and is resistant to bending whilepermitting some bending, depending on the thickness of the shaft. Inexample, drill bit can be fabricated from stainless steel. In anexample, drill bit 16 is fabricated from 465 Stainless Steel per ASTMF899.

As shown in FIGS. 3A and 3B, cutting head 50 can include cutting edge 62that forms the axial rake angle α2. Cutting edge 62 can be disposed atgash angle α1. Additionally, flutes 58A and 58B can form point angle α3.First drive shaft 52 can have a first diameter of 01 and second driveshaft 56 can have a second diameter of Ø2. First diameter Ø1 can belarger than second diameter Ø2 to, for example, help ensure that bendingwill occur along second drive shaft 56 before or in place of any bendingof first drive shaft 52. In an example, first drive shaft 52 can have afirst diameter Ø1 of approximately 4.47 mm and second drive shaft 56 canhave a second diameter Ø2 of approximately 1.5 mm. The present inventorshave found that a second diameter Ø2 of 1.5 mm is well suited forbending and transmitting vibration without sacrificing too muchstrength. In examples, second diameter Ø2 can be in a range of +/−0.5 mmof 1.5 mm. Second drive shaft 56 can be in a range of +/−0.5 mm of 4.47mm. However, other diameters for first diameter Ø1 and second diameterØ2 can be used to generate desirable bending of second drive shaft 56 asdescribed herein. In examples, flexible drill bit can have threedifferent sections, each with varying lengths designed to maximizestrength, flexibility and vibration transmission, a drill tip section, aflexible section and a stiffer shaft section for coupling to driver. Inan example, second drive shaft 56 can have a length L1 of approximately32.6 mm, however other lengths can be used to generate desirable bendingof second drive shaft 52 as described herein. First drive shaft 56 andsecond drive shaft 56 can be connected at a necked-down, tapered orsmooth transition region or section. In an example, neck 54 can includea curved surface 60 that can have a radius RI of approximately 40 mm.Curved surface 60 can be tangent to the outer surface of second driveshaft 56. Cutting head 50 can be provided with tip 68 having gash anglesα1 and α2 that provides desirable cutting features, such as areconducive to reaming bone in a smooth matter without generatingvibration that interferes with vibrations being transmitted throughsecond drive shaft 56. In an example, gash angle α1 can be approximately24°+/−2°. In an example, rake angle α2 can be approximately 7°+/−2°. Inan example, point angle α3 can be approximately 81.8°. The presentinventors have found that the foregoing combination of features providessufficient flexibility in second drive shaft 56 to transmit the feel ofcutting edge 62 engaging bone through first drive shaft 52 to a user ofpowered driver 12 at handle 20 (FIG. 1).

FIG. 5 is a close-up side view of cutting head 50 and flexible shaft 56of FIG. 2 showing indicators 63 comprising graduation marks 64A-64F andgraduation bands 66A-66E that can be used for depth control. Graduationmarks 64A-64F can be used to indicate the length of flexible drill bit16 from tip 68 to the specific graduation mark. Indicia 70A and 70B canbe included on drive shaft 56 to indicate the magnitude of eachgraduation mark, such as with Arabic numerals. For example, each ofgraduation marks 64A-64F indicate a depth of a half a centimeter, withgraduation mark 64A indicating a depth of 2.5 cm and graduation mark 64Findicating a depth of 5.0 cm. Thus, each band can encompass acorresponding 0.5 cm. Each of bands 64A-64F can further includeadditional half marks to indicate smaller depth increments, such asmillimeters. For example, band 64C can include hash marks 74. Thevarious graduation bands, graduation marks and hash marks can correspondto the lengths of fastener shafts of bone anchors commonly used inpedicle screw implantation procedures.

FIG. 6 is an exploded view of powered driver 12 of FIG. 1 shown withgear system 74, pedicle screw driver shaft 76, sliding sleeve 78 andpedicle screw 80. Powered driver 12 can function as describedpreviously. Gear system 74 can comprise teeth 82 and socket 84. Drivershaft 76 can comprise coupler 86, shaft 88 and tip 90. Pedicle screw 80can comprise head 92, threaded shaft 94 and housing 96.

Teeth 44 of gear system socket 24 can be configured to mate with teeth82 of gear system 74. Gear system 74 can operate in a similar manner asgear system 14, but can include a different socket than drill bit socket32. For example, gear system 74 can include driver socket 84, which canbe configured to mate with coupler 86 of driver shaft 76. Coupler 86 caninclude features to transmit torque from gear system 74 to shaft 88 ofdriver shaft 76 and to prevent driver shaft 76 from being axiallyseparated from gear system 74. Gear system 74 can additionally includegearing that is different than gear system 14 to provide differentrotational output speeds for driver shaft 76 that can be more conducivefor driving pedicle screw 80 as compared to rotational output speedsthat are more conducive for tapping and drilling operations. Drivershaft 76 can also include driver tip 90 that can be configured to matewith a corresponding socket (not visible in FIG. 6) in head 92 ofpedicle screw 80. In an example, tip 90 can comprise a hexalobe driver.Pedicle screw 80 can also include threaded shaft 94 that can extend fromhead 92 to engage with boney structure of a pedicle of a vertebra.Housing 96 can be coupled to head 92 to receive a rod or other supportstructure that is to be attached to the vertebra via pedicle screw 80.Sleeve 78 can be configured to slide onto driver shaft 76 by slippingover tip 90. Sleeve 78 can be used as a handle for a surgeon or otheroperator of system 10 to grasp driver shaft 76 while implanting pediclescrew 80 to guide or steady driver shaft 76.

In embodiments, sleeve 78 can be configured to mount and slide ontoflexible drill bit 16, such as at drive shaft 52. As discussed herein,sleeve 78 can be used to guide and steady flexible drill bit 16.Additionally, sleeve 78 can be configured to assist in sensing vibrationfrom flexible drill bit 16 to, for example, eliminate having to sensevibration through powered driver 12 at handle 20.

FIG. 7 is a perspective view of sleeve 78 of FIG. 6. Sleeve 78 cancomprise main body 100, first end 102, second end 104, through-bore 106,first cut-outs 108, second cut-outs 110, first rib 112, second rib 114(FIG. 9) and flutes 116. FIG. 8 is a side cross sectional view of sleeve78 of FIG. 7 taken at section 8-8. FIG. 9 is an end cross-sectional viewof sleeve 78 of FIG. 7 take at section 9-9. FIGS. 7-9 are discussedconcurrently.

Sleeve 78 can be made of a single piece of material defined by main body100. In an example, sleeve 78 can be fabricated from a polymer material.In examples, the material is non-abrasive and resilient. Main body 100can be generally cylindrical in shape. As can be seen in FIG. 9, outersurface 118 of main body 100 can be circular, but for flutes 116. Flutes116 can form edges along part of the length of main body 100 thatprovide grip-enhancements. First cut-outs 108 and second cut-outs 110can extend into main body from ends 102 and 104, respectively, toprovide sleeve 78 with a degree of flexibility or springiness towardends 102 and 104. Through-bore 106 can extend all the way through mainbody 100 from first end 102 to second end 104. Through-bore 106 can havea diameter Ø3 that can be approximately the same diameter as drivershaft 76, or slightly larger. Ribs 112 and 114 can extend from innersurface 120 of through-bore 106. Main body 100 can flex outward alongcut-outs 108 and cut-outs 110. With main body 100 not flexed, thediameter of through-bore 106 at ribs 112 and 114 can be smaller than thediameter of driver shaft 76. When sleeve 78 is positioned onto drivershaft 76, driver shaft 76 will push against ribs 112 and 114, causingmain body to flex at cut-outs 108 and 110. Thus, ribs 112 and 114 willbe pushed into engagement with driver shaft 76 to support sleeve 78.With diameter Ø3 being slightly larger than the diameter of driver shaft76, inner surface 120 will be spaced from driver shaft 76 so that sleeve78 is mostly floating relative to driver shaft 76, but for the presenceof ribs 112 and 114.

Main body 100 is configured to freely slide along the length of drivershaft 76 (FIG. 6). Ribs 112 and 114 can be used to space main body 100from the outer surface of driver shaft 76 to reduce frictiontherebetween so that sleeve 78 more readily floats relative to drivershaft 76. As such, ribs 112 and 114 provide a friction fit orinterference fit with driver shaft 76 to permit sleeve 78 to support theweight of sleeve 78. As such, without being acted upon, sleeve 78 willremain in position along driver shaft 76 unless acted upon by a surgeonor operator of system 10. Thus, a surgeon can slide sleeve 78 axiallyalong the length of driver shaft 76. Additionally, a surgeon can gripsleeve 78 while applying rotational power to driver shaft 76 frompowered driver 12 (FIG. 6) and driver shaft 76 can rotate within sleeve78 while sleeve 78 is gripped. As such, a surgeon can hold onto sleeve78 to steady drive shaft 76 and more accurately guide pedicle screw 80into the target site on the bone. Flutes 116 can inhibit sleeve 78 fromslipping within the hand of the surgeon. In additional embodiments, ribs112 and 114 can be used to couple with features of driver shaft 76 toaxially lock sleeve 78 in place. For example, ribs 112 and 114 can slipinto grooves provided along driver shaft 76 to position sleeve 78 in adesired location along driver shaft 76, such as near coupler 86, toposition sleeve 78 out of the way, or near tip 90, to position sleeve 78in an advantageous position for pedicle screw guidance.

FIG. 10 is a diagrammatic superior view of a cross-section of vertebra122 showing probe 124 inserted into pedicle 126 for preparation of apilot drill bit. Vertebra 122 includes pedicle 126, lamina 128, spinousprocess 130, transverse process 132, vertebral foramen 134 and body 136.Vertebra 122 is comprised of outer cortical bone 138 and innercancellous bone 140. As is understood in the art, cancellous bone 140 issofter and less dense than cortical bone. Pedicle 126 at least partiallydefines a narrow passage of bone between vertebral foramen 134 and theexterior of vertebra 122. Pedicel 126 thus includes an even narrowerpassage of cancellous bone 140 therein, identified in FIG. 10 ascancellous bone canal 126A. Cancellous bone canal 126A can be bound byouter cortical wall 126B and interior cortical walls 126C and 126D. Asis known in the art, nerve tissue including the spinal cord is locatedwithin vertebral foramen 134. As such, it is desirable to avoidpenetrating into vertebral foramen 134 with pedicle screw 80. Thus, itis desirable to insert pedicle screw 80 into pedicle 126 straight alonga trajectory coincident with axis A_(P).

Probe 124 can comprise handle portion 142 and probe portion 144, whichterminates at tip 146. Probe portion 144 can be curved as shown in FIG.10 such that tip 146 can extend along axis A_(P), while handle portion142 is angled relative to axis A_(P). Probe 124 is configured for manualoperation by a surgeon or operator of system 10. As such, handle portion142 can comprise an elongate shaft for manipulation by the hand of thesurgeon. Conventionally, a surgeon would use probe 124 to prepare anentry site for a reamer, tap and pedicel screw. However, with curvedprobes, such as probe 124, surgeons have a tendency to medialize thetrajectory of the probe due to the curve. Medializing the probe canpotentially incur the risk of medial breach of vertebral foramen 134.With the use of flexible drill bit 16, a pilot hole can be drilled, asdiscussed with reference to FIG. 11, without having to medialize drillbit 16. As such probe 124 need not be used to form a pilot hole invertebra 122. However, probe 124, or an awl, power bur, curette, or adifferent straight probe can be used to make anatomic marking onvertebra 122. For example, probe 124 can be used to make a smallcentering hole or dimple in pedicle 126 in which flexible drill bit 16can be positioned to prevent flexible drill bit 16 from running off ofvertebra 122 when power is applied to drill bit 16. In an example, thecentering hole can penetrate through the outer cortical bone 138 toprovide an unobstructed path to cancellous bone 140.

FIG. 11 is a diagrammatic view of a cross-section of vertebra 122 ofFIG. 10 showing flexible drill bit 16 of FIGS. 2-5 inserted into pedicle126 to form pilot hole 148. Tip 68 can be positioned in the centeringhole formed with probe 124 in FIG. 10, though a centering hole need notbe used. Power can be applied to drill bit 16 using powered driver 12 ofFIG. 1. In order to find the natural path of cancellous bone 140 withinpedicle 126 along cancellous bone canal 126A, drill bit 16 can berotated at very slow speeds, about one to three rotations or revolutionsper second, and minimal force can be applied by the surgeon on powereddriver 12 to hold drill bit 16 against vertebra 122. As such, cuttinghead 50 of drill bit can remove bone from the centering hole and willremove cancellous bone 140 after any cortical bone 138 at outer corticalwall 126B is removed. Drill bit 16 will continue to remove cancellousbone 140 as powered driver 12 is pushed into pedicel 126. If drill bit16 becomes misaligned from axis A_(P), cutting head may engage corticalbone 138 within pedicle 126 at interior cortical wall 126C or interiorcortical wall 126D. Flexible drill bit 16 can transmit the force of theimpact of cutting head 50 on cortical bone 138 through second driveshaft 56 all the way through drill bit 16 to powered driver 12, wherethe surgeon can receive a tactile input of the impact. For example, thesurgeon can feel a vibration through handle 20 (FIG. 1). As such, thesurgeon can reposition powered driver 12 to realign drill bit 16 alongaxis A_(P). The diameter of second drive shaft 56 relative to the sizeof cutting head 50 and first drive shaft 52 permits the force of theimpact of cutting head 50 on cortical bone 138 to be transmitted tofirst drive shaft 52 via vibration. Additionally, the size and shape ofdrive shaft 56 permits drive shaft 56 to flex and bend in reaction toimpacting cortical bone 138 such that cutting head 50 deflects away fromcortical bone 138. After maintaining or correcting the orientation ofdrill bit 16 along axis A_(P), drill bit 16 can be pushed into vertebraalong axis A_(P) until the desired depth is reached. Indicators 63 canbe used to determine that the desired depth has been reached. In variousexamples, drill bit 16 can be penetrated into pedicle 126 to a depth inthe range of approximately 1.5 cm to approximately 5.0 cm. After drillbit 16 is removed, a ball tip probe (not shown) or a sounding probe suchas the one shown in FIG. 14, can be inserted into pilot hole 148 toconfirm the integrity of pedicel 126. For example, the ball tip probecan be moved around within pilot hole 148 so that a surgeon can manuallyfell if pedicle 126 has been or not been breached and that the depth isappropriate, such as for the desired pedicle screw, e.g., pedicle screw80.

In an example, cutting head 50 of drill bit 16 can be smaller than thediameter of threaded shaft 94 of pedicle screw 80, as is shown in FIGS.11 and 15. In an example, bone canals produced by cutting head 50 can bein the range of approximately 1.5 mm to 2. 5 mm for such configurations.In such cases, the bone canal formed by drill bit 16 can be widened viaanother enlarging drill bit having a cutting head with a diameterapproximating that of threaded shaft 94 of pedicle screw or a bluntended reamer having a cutting diameter approximating that of threadedshaft 94, such as reamer probe 150 of FIG. 12. Drill bits used forenlarging or widening of a bone canal already formed can additionallyinclude flexible fastener shafts described herein, e.g. having one orboth of a tapered shaft and a bulbous cutting head. In examples,flexible drill bits used in combination with these enlarging drill bitsand blunt ended reamers can have diameters in the range of about 2.0 mmto 3.0 mm. In other examples, cutting head 50 of drill bit 16 can besized to have a diameter approximating that of threaded shaft 94 ofpedicle screw 80 to be attached to the vertebra, such as approximately2.0 mm up to the largest diameter fastener used in spinal procedures,e.g. 3.0 mm, and can have one or both of a tapered shaft and a bulbouscutting head.

FIG. 12 is a diagrammatic view of a cross-section of vertebra 122 ofFIG. 11 showing reamer probe 150 inserted into pilot hole 148 of FIG. 11to widen pilot hole 148. Reamer probe 150 can comprise drive shaft 152,drill portion 154, blunt tip 156 and indicators 158. Reamer probe 150can be used to widen a portion of the length of pilot hole 148 extendinginto cortical bone 138.

Reamer probe 150 can be used to expand, or further dilate, pilot hole148 and produce a straight trajectory along axis A_(P). Reamer probe 150can comprise drive shaft 152 that can couple to a gear system, such asgear systems 14 or 74, and drill portion 154 that can cut into pilothole 148. Drill portion 154 has a wider diameter than cutting head 50.In an example, drill portion 154 has a diameter that corresponds to theminor diameter of threaded shaft 94 (i.e., the diameter of shaft 94 notincluding the thread) of pedicle screw 80. Reamer probe 150 can alsocomprise blunt tip 156 that can be configured to not cut bone. Reamerprobe 150 can be advanced with approximately the same force thatflexible drill bit 16 is advanced and at approximately the samerotational speed to avoid damaging or penetrating cortical bone 138.Reamer probe 150 can self-center within pilot hole 148. Blunt tip 156can have a length that can span the region of cancellous bone 140 withinbody 136 of vertebra 122 for pilot hole 148. In other words, when reamerprobe 150 is fully inserted into pilot hole 148, blunt tip 156 willengage the end of pilot hole 148 and extend across cancellous bone 140while drill portion 154 spans across cortical bone 138 to widen pilothole 148 to a new, larger diameter. In an example, drill portion 154 canbe configured to extend over the first 20 mm of the length of threadedshaft 94 (measured from head 92) of pedicle screw 80 (FIG. 6) becausecancellous bone 140 of vertebra 122 does not need to be widened toreceive threaded shaft 94. Indicators 158, which can be configured thesame as indicators 63, can be used to determine or verify the depth ofwidened pilot hole 148. In various examples, reamer probe 150 can bepenetrated into pedicle 126 to a depth in the range of approximately 1.5cm to approximately 5.0 cm. Sliding sleeve 78 can additionally beconfigured for use with reamer probe 150.

FIG. 13 is a diagrammatic view of a cross-section of vertebra 122 ofFIG. 12 showing tap 160 inserted into widened pilot hole 148 to formthreading on pedicle screw hole 162. Tap 160 can comprise drive shaft164, tap portion 166 and indicators 168. Drive shaft 164 can be coupledto powered driver as described herein to rotate tap portion 166. Tapportion 166 can include cutting edges to cut thread channels intopedicle screw hole 162, particularly along cortical bone 138. The threadchannels can be configured to mate with thread on threaded shaft 94 ofpedicle screw 80 (FIG. 6). In various examples, tap 160 can bepenetrated into pedicle 126 to a depth in the range of approximately 1.5cm to approximately 5.0 cm. Tap 160 can be removed from pedicle screwhole 162 by rotating drive shaft 164 is reverse using powered driver 12.As such, pedicle screw hole 162 is in a prepared condition for receivingpedicle screw 80. However, not all of the steps described with referenceto FIGS. 12 and 13 need be performed to couple pedicle screw 80 tovertebra 122. For example, threaded shaft 94 can be directly threadedinto pilot hole 148. Sliding sleeve 78 can additionally be configuredfor use with tap 160.

FIG. 14 is a diagrammatic view of a cross-section of vertebra 122 ofFIG. 13 showing sounding probe 170 inserted into pedicle screw hole 162of FIG. 13 to confirm pedicle integrity of pedicle screw hole 162.Sounding probe 170 may be used at any point after drilling usingflexible drill bit 16 in the pedicle preparation process to confirmpedicle integrity, trajectory, and/or threads tapped into vertebra 122.Sounding probe 170 can comprise a small-diameter blunt instrument thatcan be manually moved around within pilot hole 148 or pedicle screw hole162 to probe cortical bone 138 to verify that cortical bone 138 isintact. After a surgeon determines that pedicle screw hole 162 is intactor otherwise finally prepared, pedicle screw 80 can be inserted therein.

FIG. 15 is a diagrammatic view of a cross-section of vertebra 122 ofFIG. 14 showing pedicle screw 80 being inserted into pedicle screw hole162 using powered driver shaft 76 with sleeve 78. Tip 90 of driver shaft76 can be inserted into a socket within head 92. A surgeon can graspsliding sleeve 78 to steady driver shaft 76 and guide tip 172 offastener shaft 94 into engagement with the opening of pedicle screw hole162. As discussed above, driver shaft 76 can be coupled to powereddriver 12 to cause rotation of pedicle screw 80 through driver shaft 76.Rotation of threaded shaft 94 can cause thread on threaded shaft 94 toengage pedicle screw hole 162, whether tapped with tap 160 (FIG. 13) ornot. Threaded shaft 94 can be rotated until head 92 engages pedicle 126.The surgeon can move sliding sleeve 78 along driver shaft 76 as threadedshaft 94 progresses into pedicle screw hole 162.

FIG. 16 is a line diagram illustrating steps of method 200 for forming apilot hole using a flexible drill bit and a powered driver in accordancewith the systems and methods described herein. The following steps arediscussed in an exemplary order, but the discussed steps may beperformed in a different order and some of the steps may be consideredoptional.

At step 202, a trajectory for a pedicle screw shaft into a cancellousbone canal of a vertebral pedicle behind a cortical bone wall can bedetermined. For example, a surgeon can review images, such as x-rayimaging, of a patient to show cancellous bone of the vertebra withincortical bone. A surgeon may also inspect the vertebra intraoperativelyto evaluate boney structures, such as a pedicle, a spinous process and atransverse process, to determine an orientation or angle of thecancellous bone canal between the spinous process and the transverseprocess.

At step 204, a centering hole can be formed in the cortical bone wall.For example, a probe or awl can be used to make a dimple or depressionin the cortical bone wall. The centering hole can be made sufficientlydeep to receive a tip of a drill bit to prevent the drill bit fromslipping off of the bone when rotated. The centering hole can penetratecompletely through the cortical bone wall.

At step 206, a shaft of a flexible drill bit can be attached to apowered driver. Engagement features of the flexible drill bit shaft canbe locked into the powered driver to receive torque from the powereddriver and prevent the flexible drill bit from separating from thepowered driver. The flexible drill bit can also include a neck portionwith a tapered profile that reduces the diameter of the shaft. The neckportion can connect to a flexible shaft portion that connects to abulbous cutting head for cutting bone. In other embodiments, the cuttinghead is not bulbous and has a diameter approximately equal to a diameterof the flexible shaft. The diameter of the cutting head can vary asdescribed herein, depending on if the flexible drill bit shaft is beingused to produce only an initial guiding hole or a final canal for thepedicle screw.

At step 208, a tip of a flexible drill bit at the bulbous cutting headcan be engaged with the cortical bone wall. The tip can be positioned ina centering hole, but need not be. A shaft of the drill bit can beoriented along a central axis of the determined cancellous bone canaltrajectory.

At step 210, the powered driver can be activated to rotate the flexibledrill bit. For example, a button of the powered driver can be depressedor partially depressed to activate an electric motor powered by abattery in the powered driver. Alternatively, the powered driver can bepowered by an external electricity source. Depression of the button cancause rotation of the flexible drill bit shaft. The flexible drill bitcan be rotated by the powered driver at a slow speed. In an example theslow speed can comprise one to three revolutions per second.

At step 212, the tip of the flexible drill bit can be pushed intoexterior cortical bone of the vertebra. The flexible drill bit can bemaintained in an orientation along the determined cancellous bone canaltrajectory. The flexible drill bit can be pushed until the exteriorcortical bone wall is penetrated.

At step 214, the flexible drill bit can be guided into cancellous bonewithin the pedicle of the vertebra. The flexible drill bit can bemaintained in the orientation along the determined cancellous bone canaltrajectory. However, it may be possible for the flexible drill bit tobecome misaligned or for the determined cancellous bone canal trajectoryto be not adequately aligned with the anatomical cancellous bone canalin the pedicle.

At step 216, a surgeon can receive tactile feedback generated with theflexible drill bit. The operator can monitor the flexible drill bit toreceive the tactile feedback. The tactile feedback can comprise areceived vibration from the flexible drill bit, a perceived change inorientation of the flexible drill bit, a perceived change in therotational speed of the flexible drill bit, or a perceived change in therate at which the flexible drill bit is advanced into the bone. Thetactile feedback can be generated by engagement of the cutting head ofthe flexible drill bit with cortical bone inside of the pedicle. Theflexible drill bit can flex or bend to prevent or inhibit the cuttinghead from penetrating straight into the cortical bone, therebyeliminating or minimizing cutting of the cortical bone and penetrationof the vertebral foramen.

At step 218, the orientation of the flexible drill bit can be adjustedto disengage the cutting head from the cortical bone. In an example, theflexible drill bit can be reoriented so as to align with the centralaxis of the determined cancellous bone canal trajectory. However, asindicated, the determined cancellous bone canal trajectory may notrepresent the actual cancellous bone canal path. As such, the flexibledrill bit can be reoriented to move the cutting head away from thesensed interior cortical bone from the tactile feedback. That is, if thesurgeon senses that the tactile feedback indicates the cutting head hasmoved medially to engage cortical bone alongside the vertebral foramen,the surgeon can move the cutting head laterally away from the vertebralforamen even if that moves the flexible drill bit off of the determinedtrajectory.

At step 220, the flexible drill bit can be advanced along the pathdetermined in step 218 to the desired depth. That is, after correctiveaction in reaction to the generated tactile feedback, the flexible drillbit can be pushed further into the cancellous bone to form a pediclescrew hole to receive a threaded fastener of a pedicle screw. The depthof the pedicle screw hole can vary as described herein, depending on ifthe flexible drill bit shaft is being used to produce only an initialguiding hole or a final canal for the pedicle screw. In examples, thepedicle screw hole depth can correspond to a length of the threadedfastener of the pedicle screw.

At step 220, the depth of the pedicle screw hole can be verified withindicators located on the flexible drill bit. The outer surface of thepedicle at the outer cortical wall can be aligned with graduation marksor graduation bands on the flexible drill bit. The surgeon can monitorprogress of the flexible drill bit against these indicators as theflexible drill bit is advanced.

At step 222, the flexible drill bit can be removed from the pediclescrew hole. Application of rotational power to the flexible drill bitfrom the powered driver can be stopped and the flexible drill bit can bewithdrawn from the vertebra. In an example, the powered driver can applyreverse rotational power to the flexible drill bit to facilitateremoval.

At step 224, the pedicle screw hole can be checked with a probe toverify the integrity of the bone. For example, the probe can be manuallymanipulated within the pedicle screw hole to look for anomalies in thebone, weak spots in the bone or holes penetrating into the vertebralforamen. If no issues are detected with the probe, the pedicle screwhole can be finished as desired by the surgeon and the pedicle screw canbe attached to the pedicel screw hole, such as by using the systems andmethods described herein. If any issues are detected, the surgeon cantake corrective action to restore the integrity of the cortical bonealong the vertebral foramen, can choose to not implant he pedicle screw,or can decide that further drilling with the flexible drill bit isrequired to straighten or deepen the pedicle screw hole. As discussedherein, the diameter of the pedicle screw hole can be widened with awidening or enlarging drill bit having a larger cutting head, a reameror an awl if a flexible drill bit having a diameter corresponding to adiameter of the pedicle screw is not used.

The systems and methods discussed in the present application can beuseful in implanting bone fasteners or pedicle screws into boneystructures of vertebra. In particular, the systems and methods allow forthe safe use of powered drill bits by preserving the ability of asurgeon to use instinct and tactile feedback to feel changes inresistance to movement of the drill bit at a powered driver. The systemsand methods include use of a flexible drill bit that is shaped andconfigured to transmit forces, such as vibrations, on a cutting head ofthe drill bit back to the surgeon through the drill bit shaft and thepowered driver. As such, the systems and methods can be effective inreducing the risk of penetrating a vertebral foramen of the vertebrawith a drill bit. As such, the systems and methods are effective inreducing potential injury to the spine and spinal cord.

Various Notes & Examples

Example 1 can include or use subject matter such as a method ofimplanting a bone anchor in a vertebra that can comprise engaging a tipof a flexible drill bit with boney structure of the vertebra, rotatingthe flexible drill bit at a slow speed, pushing the drill bit intoexterior cortical bone of the boney structure of the vertebra, guidingthe flexible drill bit into cancellous bone of the vertebra, receiving atactile output generated by the flexible drill bit indicating resistanceof interior cortical bone of the boney structure through the flexibledrill bit, and reorienting a trajectory of the flexible drill bit towardthe cancellous bone of the vertebra in reaction to the tactile output.

Example 2 can include, or can optionally be combined with the subjectmatter of Example 1, to optionally include rotating the flexible drillbit at a slow speed with a powered driver.

Example 3 can include, or can optionally be combined with the subjectmatter of one or any combination of Examples 1 or 2 to optionallyinclude rotating the flexible drill bit at approximately one to threerevolutions per second.

Example 4 can include, or can optionally be combined with the subjectmatter of one or any combination of Examples 1 through 3 to optionallyinclude receiving tactile output at the powered driver by feelingvibration of the flexible drill bit.

Example 5 can include, or can optionally be combined with the subjectmatter of one or any combination of Examples 1 through 4 to optionallyinclude feeling vibration of the flexible drill bit by feeling bendingof the flexible drill bit.

Example 6 can include, or can optionally be combined with the subjectmatter of one or any combination of Examples 1 through 5 to optionallyinclude bending of the flexible drill bit by bending the flexible drillbit between a necked-down shaft portion and a bulbous drill tip.

Example 7 can include, or can optionally be combined with the subjectmatter of one or any combination of Examples 1 through 6 to optionallyinclude engaging the tip of the flexible drill bit with the boneystructure of the vertebra by forming a centering hole in the exteriorcortical bone of the boney structure, and engaging the tip of theflexible drill bit with the centering hole.

Example 8 can include, or can optionally be combined with the subjectmatter of one or any combination of Examples 1 through 7 to optionallyinclude withdrawing the flexible drill bit from the boney structure toleave a bone canal, and confirming formation of the bone canal with aball tip probe.

Example 9 can include, or can optionally be combined with the subjectmatter of one or any combination of Examples 1 through 8 to optionallyinclude withdrawing the flexible drill bit from the boney structure toleave a bone canal, widening the bone canal with an enlarging drill bitto a diameter of a threaded fastener of the bone anchor, and insertingthe threaded fastener into the widened bone canal.

Example 10 withdrawing the flexible drill bit from the boney structureto leave a bone canal, widening the bone canal with a reamer to adiameter of a threaded fastener of the bone anchor, inserting thethreaded fastener into the widened bone canal.

Example 11 can include, or can optionally be combined with the subjectmatter of one or any combination of Examples 1 through 9 to optionallyinclude withdrawing the flexible drill bit from the boney structure toleave a bone canal, and inserting the bone anchor into the bone canal,wherein a flexible drill bit has a diameter corresponding to thethreaded shaft of the bone anchor.

Example 12 can include, or can optionally be combined with the subjectmatter of claim 11 to optionally include checking a depth of theflexible drill bit in the vertebra by referencing cortical bone againstindicia provided on a flexible portion of the flexible drill bit.

Example 13 can include, or can optionally be combined with the subjectmatter of one or any combination of Examples 1 through 12 to optionallyinclude inserting the bone anchor into the bone canal by coupling asleeve to a driver shaft, coupling the driver shaft to the bone anchor,grasping the sleeve, guiding the driver shaft toward the boney structureto insert the bone anchor into the bone canal, rotating the driver shaftwithin the sleeve using a powered driver and translating the sleevealong the driver shaft to guide the bone anchor to the bone canal and toreceive the tactile output of the flexible drill bit.

Example 14 can include or use subject matter such as a method ofimplanting a pedicle screw into a pedicle of a vertebra that cancomprise determining a trajectory for a pedicle screw shaft into acancellous bone canal behind a cortical bone wall to avoid interiorcortical bone, engaging a tip of a drill bit having a tapered shaft witha starting point of the trajectory on the cortical bone wall of thepedicle of the vertebra, rotating the drill bit using rotational inputfrom a powered driver, pushing the powered driver to penetrate the tipof the drill bit through the cortical bone wall along the trajectory,guiding the drill bit into the cancellous bone canal, sensing engagementof the tip of the drill bit with the interior cortical bone, andreorienting the drill bit along the trajectory away from the interiorcortical bone.

Example 15 can include, or can optionally be combined with the subjectmatter of Example 14, to optionally include producing a centering holein the cortical bone wall at the starting point before engaging the tipof the drill bit with the cortical bone wall.

Example 16 can include, or can optionally be combined with the subjectmatter of one or any combination of Examples 14 or 15 to optionallyinclude sensing engagement of the tip of the drill bit by receiving atactile feedback at the powered driver.

Example 17 can include, or can optionally be combined with the subjectmatter of one or any combination of Examples 14 through 16 to optionallyinclude tactile feedback that can comprise a vibration of the drill bittransmitted to the powered driver.

Example 18 can include, or can optionally be combined with the subjectmatter of one or any combination of Examples 14 through 17 to optionallyinclude a drill bit comprising a first shaft portion for coupling to adriver, a tapered portion extending from the first shaft portion at afirst end to a reduced diameter at a second end, and a second shaftportion extending from the second end of the tapered portion, the secondshaft portion having a diameter of in the range of 1.0 mm to 2.0 mm,wherein the vibration of the drill bit is caused by bending of thesecond shaft portion of the drill bit.

vibration of the drill bit that can be caused by bending of anecked-down shaft of the drill bit.

Example 19 can include, or can optionally be combined with the subjectmatter of one or any combination of Examples 14 through 18 to optionallyinclude bending of the necked-down shaft of the drill bit that can causethe tip of the drill bit to deflect away from the interior corticalbone.

Example 20 can include, or can optionally be combined with the subjectmatter of one or any combination of Examples 13 through 19 to optionallyinclude withdrawing the flexible drill bit from the vertebra to leave abone canal, confirming formation of the bone canal with a ball tipprobe, and inserting a bone anchor into the bone canal.

Each of these non-limiting examples can stand on its own, or can becombined in various permutations or combinations with one or more of theother examples.

The above detailed description includes references to the accompanyingdrawings, which form a part of the detailed description. The drawingsshow, by way of illustration, specific embodiments in which theinvention can be practiced. These embodiments are also referred toherein as “examples.” Such examples can include elements in addition tothose shown or described. However, the present inventor alsocontemplates examples in which only those elements shown or describedare provided. Moreover, the present inventor also contemplates examplesusing any combination or permutation of those elements shown ordescribed (or one or more aspects thereof), either with respect to aparticular example (or one or more aspects thereof), or with respect toother examples (or one or more aspects thereof) shown or describedherein.

In the event of inconsistent usages between this document and anydocuments so incorporated by reference, the usage in this documentcontrols.

In this document, the terms “a” or “an” are used, as is common in patentdocuments, to include one or more than one, independent of any otherinstances or usages of “at least one” or “one or more.” In thisdocument, the term “or” is used to refer to a nonexclusive or, such that“A or B” includes “A but not B,” “B but not A,” and “A and B,” unlessotherwise indicated. In this document, the terms “including” and “inwhich” are used as the plain-English equivalents of the respective terms“comprising” and “wherein.” Also, in the following claims, the terms“including” and “comprising” are open-ended, that is, a system, device,article, composition, formulation, or process that includes elements inaddition to those listed after such a term in a claim are still deemedto fall within the scope of that claim. Moreover, in the followingclaims, the terms “first,” “second,” and “third,” etc. are used merelyas labels, and are not intended to impose numerical requirements ontheir objects.

Method examples described herein can be machine or computer-implementedat least in part. Some examples can include a computer-readable mediumor machine-readable medium encoded with instructions operable toconfigure an electronic device to perform methods as described in theabove examples. An implementation of such methods can include code, suchas microcode, assembly language code, a higher-level language code, orthe like. Such code can include computer readable instructions forperforming various methods. The code may form portions of computerprogram products. Further, in an example, the code can be tangiblystored on one or more volatile, non-transitory, or non-volatile tangiblecomputer-readable media, such as during execution or at other times.Examples of these tangible computer-readable media can include, but arenot limited to, hard disks, removable magnetic disks, removable opticaldisks (e.g., compact disks and digital video disks), magnetic cassettes,memory cards or sticks, random access memories (RAMs), read onlymemories (ROMs), and the like.

The above description is intended to be illustrative, and notrestrictive. For example, the above-described examples (or one or moreaspects thereof) may be used in combination with each other. Otherembodiments can be used, such as by one of ordinary skill in the artupon reviewing the above description. The Abstract is provided to complywith 37 C.F.R. § 1.72(b), to allow the reader to quickly ascertain thenature of the technical disclosure. It is submitted with theunderstanding that it will not be used to interpret or limit the scopeor meaning of the claims. Also, in the above Detailed Description,various features may be grouped together to streamline the disclosure.This should not be interpreted as intending that an unclaimed disclosedfeature is essential to any claim. Rather, inventive subject matter maylie in less than all features of a particular disclosed embodiment.Thus, the following claims are hereby incorporated into the DetailedDescription as examples or embodiments, with each claim standing on itsown as a separate embodiment, and it is contemplated that suchembodiments can be combined with each other in various combinations orpermutations. The scope of the invention should be determined withreference to the appended claims, along with the full scope ofequivalents to which such claims are entitled.

The claimed invention is:
 1. A method of implanting a bone anchor in avertebra, the method comprising: engaging a tip of a flexible drill bitwith boney structure of the vertebra; rotating the flexible drill bit ata slow speed; pushing the drill bit into exterior cortical bone of theboney structure of the vertebra; guiding the flexible drill bit intocancellous bone of the vertebra; receiving a tactile output generated bythe flexible drill bit indicating resistance of interior cortical boneof the boney structure through the flexible drill bit; and reorienting atrajectory of the flexible drill bit toward the cancellous bone of thevertebra in reaction to the tactile output.
 2. The method of claim 1,wherein rotating the flexible drill bit at a slow speed comprisesrotating the flexible drill bit with a powered driver.
 3. The method ofclaim 2, wherein rotating the flexible drill bit at a slow speedcomprises rotating the flexible drill bit at approximately one to threerevolutions per second.
 4. The method of claim 2, further comprisingreceiving the tactile output at the powered driver by feeling vibrationof the flexible drill bit.
 5. The method of claim 4, wherein feelingvibration of the flexible drill bit comprises feeling bending of theflexible drill bit.
 6. The method of claim 5, wherein bending of theflexible drill bit comprises bending the flexible drill bit between anecked-down shaft portion and a bulbous drill tip.
 7. The method ofclaim 1, wherein engaging the tip of the flexible drill bit with theboney structure of the vertebra further comprises: forming a centeringhole in the exterior cortical bone of the boney structure; and engagingthe tip of the flexible drill bit with the centering hole.
 8. The methodof claim 1, further comprising: withdrawing the flexible drill bit fromthe boney structure to leave a bone canal; and confirming formation ofthe bone canal with a ball tip probe.
 9. The method of claim 1, furthercomprising: withdrawing the flexible drill bit from the boney structureto leave a bone canal; widening the bone canal with an enlarging drillbit to a diameter of a threaded fastener of the bone anchor; andinserting the threaded fastener into the widened bone canal.
 10. Themethod of claim 1, further comprising: withdrawing the flexible drillbit from the boney structure to leave a bone canal; widening the bonecanal with a reamer to a diameter of a threaded fastener of the boneanchor; and inserting the threaded fastener into the widened bone canal.11. The method of claim 1, further comprising: withdrawing the flexibledrill bit from the boney structure to leave a bone canal; and insertinga bone anchor into the bone canal, wherein the flexible drill bit has adiameter corresponding to a threaded shaft of the bone anchor.
 12. Themethod of claim 1, further comprising checking a depth of the flexibledrill bit in the vertebra by referencing cortical bone against indiciaprovided on a flexible portion of the flexible drill bit.
 13. The methodof claim 10, wherein inserting the bone anchor into the bone canalcomprises: coupling a sleeve to a driver shaft; coupling the drivershaft to the bone anchor; grasping the sleeve; guiding the driver shafttoward the boney structure to insert the bone anchor into the bonecanal; rotating the driver shaft within the sleeve using a powereddriver; and translating the sleeve along the driver shaft to guide thebone anchor to the bone canal and to receive the tactile output of theflexible drill bit.
 14. A method of implanting a pedicle screw into apedicle of a vertebra, the method comprising: determining a trajectoryfor a pedicle screw shaft into a cancellous bone canal behind a corticalbone wall to avoid interior cortical bone; engaging a tip of a drill bithaving a tapered shaft with a starting point of the trajectory on thecortical bone wall of the pedicle of the vertebra; rotating the drillbit using rotational input from a powered driver; pushing the powereddriver to penetrate the tip of the drill bit through the cortical bonewall along the trajectory; guiding the drill bit into the cancellousbone canal; sensing engagement of the tip of the drill bit with theinterior cortical bone; and reorienting the drill bit along thetrajectory away from the interior cortical bone.
 15. The method of claim14, further comprising producing a centering hole in the cortical bonewall at the starting point before engaging the tip of the drill bit withthe cortical bone wall.
 16. The method of claim 14, wherein sensingengagement of the tip of the drill bit comprises receiving a tactilefeedback at the powered driver.
 17. The method of claim 16, wherein thetactile feedback comprises a vibration of the drill bit transmitted tothe powered driver.
 18. The method of claim 17, wherein the drill bitcomprises: a first shaft portion for coupling to a driver; a taperedportion extending from the first shaft portion at a first end to areduced diameter at a second end; and a second shaft portion extendingfrom the second end of the tapered portion, the second shaft portionhaving a diameter of in the range of 1.0 mm to 2.0 mm; wherein thevibration of the drill bit is caused by bending of the second shaftportion of the drill bit.
 19. The method of claim 18, wherein bending ofthe necked-down shaft of the drill bit causes the tip of the drill bitto deflect away from the interior cortical bone.
 20. The method of claim14, further comprising: withdrawing the flexible drill bit from thevertebra to leave a bone canal; confirming formation of the bone canalwith a ball tip probe; and inserting a bone anchor into the bone canal.